MAINTAINERS: hwmon: Add Documentation/devicetree/bindings/hwmon

The hardware monitoring mailing list should be copied for changes
in hwmon devicetree bindings.
Signed-off-by: NGuenter Roeck <linux@roeck-us.net>

MAINTAINERS

@@ -6218,6 +6218,7 @@ L:	linux-hwmon@vger.kernel.org
 W:	http://hwmon.wiki.kernel.org/
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/groeck/linux-staging.git
 S:	Maintained
+F:	Documentation/devicetree/bindings/hwmon/
 F:	Documentation/hwmon/
 F:	drivers/hwmon/
 F:	include/linux/hwmon*.h